In recent years, high-definition display devices have been required. For example, full high-definition (1920×1080 pixels) has been in the mainstream of home-use television devices (also referred to as televisions or television receivers). From now on, 4K (3840×2160 pixels) and 8K (7680×4320 pixels) will also be spread with the development of high-definition television devices.
High-definition display panels of portable information terminals, such as mobile phones, smartphones, and tablets, have also been developed.
Typical examples of the display device include a liquid crystal display device; a light-emitting device including a light-emitting element such as an organic electroluminescent (EL) element or a light-emitting diode (LED); and electronic paper performing display by an electrophoretic method or the like.
For example, an organic EL element has a basic structure in which a layer containing a light-emitting organic compound is provided between a pair of electrodes. The light-emitting organic compound can emit light by voltage application to the element. A display device including such an organic EL element needs no backlight which is necessary for a liquid crystal display device and the like and thus can have advantages such as thin, lightweight, high contrast, and low power consumption. Patent Document 1, for example, discloses an example of a display device using an organic EL element.